This invention is directed to a step motor for use in a quartz crystal electronic wristwatch, and, in particular, to an improved rotor support assembly for reducing the load on the rotor when same is incrementally rotated through each rotary position and thereby increasing the driving torque of the rotor.
In samll-sized electronic wristwatched utilizing a quartz crystal vibrator as a time standard and a step motor for driving the clock hands, the driving torque of the rotor is usually lower than the driving torque of a step motor utilized in a mechanical wristwatch. This reduction in driving torque is often a result of the differences in size between the component parts of the electronic wristwatch and mechanical wristwatch, and the limitations placed on the electronic wristwatch movement by the capacity of the battery. Efforts have been made to reduce the loading on the rotor provided by the gear train driven by the rotor, in order to more efficiently utilize the driving torque of the rotor. Nevertheless, it is often the loading on the rotor, provided by the step motor mechanism, that diminishes the driving torque of the rotor. Accordingly, a step motor for use in an electronic wristwatch wherein the rotor support assembly substantially reduces the load on the rotor, to thereby increase the effect of the driving torque of the rotor on the gear train of the wristwatch, is desired.